In recent years, the hard carbon coating is attracting attention because it has excellent properties, e.g., high hardness, high insulation, high thermal conductivity and chemical stability, similar to those of diamond. For the formation of the hard carbon coating, already, the physical vapor deposition method (hereinafter referred to as "PVD"), such as the ion beam method, the sputtering method and the ion plating method, the ECR (Electron Cyclotron Resonance) and the RF (Radio Frecuency) plasma chemical-vapor deposition method (hereinafter referred to as "RFP-CVD") have been brought into practical use.
Generally, a compressive stress as high as about 10.sup.10 dyne/cm.sup.2 remains in the hard carbon coatings formed by the above methods. Therefore, the base material provided with the hard carbon coating formed by any of the above methods has such drawbacks that the adhesion between the hard carbon coating and the base material, especially when the base material is composed of a metal, is so poor that peeling or cracking is caused to shorten its life, or the formation of the hard carbon coating on the base material is infeasible. That is, although the hard carbon coating can be formed on the surface of a silicon base material or a super hard material by any of the above methods, it is difficult to form the hard carbon coating on the surface of any of various metal base materials, such as stainless steel base materials. Therefore, the problem exists that the types of the base materials on which the hard carbon coating can be formed are very limited.
In Japanese Patent Laid-Open Publication No. 116767/1987 (Japanese Patent Application No. 256426/1985), the inventors proposed a hard carbon coating-clad base material in which an intermediate layer composed of a lower layer mainly composed of chromium or titanium, formed on the surface of a base material by a dry plating process, and an upper layer mainly composed of silicon or germanium, formed on the surface of the lower layer by a dry plating process, is disposed between a metal base material and the hard carbon coating. Further, the inventors also proposed in Japanese Patent Laid-Open Publication No. 149673/1990 (Japanese Patent Application No. 301829/1988) a hard carbon coating-clad base material in which a solid solution layer is formed at the interface of the above upper and lower layers constituting the intermediate layer by counter diffusion.
However, still in the hard carbon coating-clad base material proposed in Japanese Patent Laid-Open Publication No. 149673/1990, the types of the base materials on which the hard carbon coating can be formed are limited. For example, when brass is employed as the base material, dezincing from the brass occurs in a vacuum atmosphere due to the rise in the temperature inside the chamber at the time of the formation of the above intermediate layer or the formation of the hard carbon coating, so that the surface of the brass base material turn into orange peel to thereby lower the corrosion resistance of the surface of the base material and the adhesion between the brass base material and the hard carbon coating. Therefore, the problem exists that, when brass is used as the base material of the hard carbon coating-clad base material proposed in Japanese Patent Laid-Open Publication No. 149673/1990, it is infeasible to fully utilize the excellent properties of the hard carbon coating.
Moreover, among iron materials Including a carbon Wool steel such as SK steel as defined in JIS G 4401 (1983), a martensitic stainless steel and ferritic stainless steel, when an iron material having poorer corrosion resistance than that of an austenitic stainless such as SUS 304 is used as the base material, corrosion due to rusting occurs in the base material after pre-wash to thereby cause the problem with respect to the adhesion between the base material and the hard carbon coating and the corrosion resistance of the hard carbon coating. The terminology "pre-wash" used herein means subjecting the base material to organic cleaning by using methylene chloride, etc., or subjecting the base material to alkaline degreasing cleaning by using alkali solution of 5-10%, and thereafter, to neutralization treatment by using nitric acid solution of 5-10%. In these pre-wash treatments, ultrasonic washer is jointly used.